DESCRIPTION The broad objective of the proposed study is to understand how the ribosomal DNA episome of Entamoeba histolytica is replicated and segregated to daughter cells. E. histolytica is an extracellular protozoan parasite responsible for amebic colitis and liver abscess, diseases that afflict upwards of 50 million people annually in the developing world. The importance of the rDNA episome derives from the fact that it is the only location of rDNA genes in Entamoeba; drugs targeted against its unique mechanisms of replication and segregation could offer new approaches to chemotherapy of amebiasis. The hypothesis is that cis acting sequences on the episome function in segregation and replication of the rDNA episome. There are 3 specific aims of the proposed study: (1) to map origins of replication on the rDNA episome of E. histolytica by 2 dimensional neutral/neutral gel electrophoresis and electron microscopy, (2) The possible existence of plasmid incompatibility between the resident rDNA episome and transfected plasmids containing sequences on the rDNA episome will be tested, and (3) To identify proteins which bind to cis-acting sequences on the rDNA episome involved in plasmid segregation/replication.